1. Field of the Invention
The present invention relates to a bit patterned medium, a reading head which reads data recorded on the bit patterned medium, and a hard disk drive (HDD) which records/reads data on/from the bit patterned medium.
2. Description of the Related Art
Since HDDs have large capacity and characteristics such as high-speed access, HDDs are widely used as data storage devices of personal computers (PCs) and various kinds of digital devices. Along with the rapid increase in the amounts of handled data due to recent technology developments, high density of HDDs is required.
HDDs generally employ a magnetic recording method for recording/reading data. A magnetic recording method is a method of recording data by magnetizing a magnetic layer of a recording medium using a magnetic field and reading data by means of a magnetic signal from magnetization of the recording medium. Magnetic recording methods can be classified into a longitudinal magnetic recording method and a perpendicular magnetic recording method. In the longitudinal magnetic recording method in which data is recorded by magnetizing a magnetic layer to be parallel to the surface of the magnetic layer, a recording density of 100 Gb/m2 can be achieved, and in the perpendicular recording method in which data is recorded by magnetizing a magnetic layer to be perpendicular to the surface of the magnetic layer, a recording density of about 500 Gb/m2 can be achieved, which is higher than that of the longitudinal magnetic recording method.
Recently, research into an electric field recording method of recording and reading data using an electric field instead of a magnetic field has been conducted. The electric field recording method is a method of recording data by polarizing a ferroelectric layer of a recording medium using an electric field and reading data by means of an electric signal using from polarization of the recording medium. According to the electric field recording method, a recording density of over 1 Tb/m2 can be achieved.
In any recording method, an increase of recording density causes a decrease in bit size, a bit being the minimum recording unit of data, and the magnitude of a signal generated from a recording medium is weakened. In order to address this problem, research into a method of increasing recording density using a patterned medium to maintain a high Signal-to-Noise Ratio (SNR) by decreasing noise from the medium also has been conducted.
FIG. 1A illustrates a schematic structure of a bit patterned medium 10. Referring to FIG. 1A, the bit patterned medium 10 includes a substrate 20 and a recording layer 30 formed on the substrate 20. The recording layer 30 includes a pattern of a plurality of bit cells 32 forming tracks of concentric circles and being physically separated from each other. A single bit is recorded in each bit cell 32, and since noise can be reduced in accordance with a small bit size, recording density can be effectively increased. According to a decrease of the bit size, the width of a reading head decreases as well. FIG. 1B is a top view illustrating the structure of the bit cells 32 of the bit patterned medium 10 together with a reading head 40. The reading head 40 reads data from each bit cell 32 of a track to be read while relatively moving along the track. In this case, the width of the reading head 40 must be sufficiently small not to generate noise due to tracks adjacent to the track to be read, and thus, the width of the reading head 40 is an important design factor as well as the width of each bit cell 32. However, reducing the width of the reading head 40 requires a very high degree of precision in a manufacturing process and thus increases manufacturing costs.